1. Field of the Invention
The present invention relates to contact materials for vacuum interrupters and to manufacturing processes therefor.
2. Description of the Prior Art
Generally, contact materials for vacuum interrupters are required to consistently satisfy the following requirements:
(a) highness in relatively large current, for example a fault current, interrupting capability,
(b) highness in dielectric strength,
(c) highness in anti-welding capability,
(d) highness in relative small leading and lagging current interrupting capability,
(e) current chopping value as small as possible.
However, contact materials to consistently satisfy all the requirements, in the present state of the art, have not been provided.
For instance, various contacts made of copper as a major constituent containing a minor constituent of a low melting point and high vapor-pressure material, such as a contact made of copper containing a 0.5 weight % bismuth (hereinafter, referred to as a Cu-0.5 Bi contact) that is disclosed by the U.S. Pat. No. 3,246,979, or a contact that is disclosed by the U.S. Pat. No. 3,596,027, are known.
Contacts made of copper containing a minor constituent of material of a low melting point and high vapor pressure such as, for example, the Cu-0.5 Bi contact, are relatively large in large current interrupting capability, electrical conductivity and anti-welding capability they are, however significantly low in dielectric strength, particularly in dielectric strength after large current interruption.
In particular, a current chopping value of a pair of the Cu-0.5 Bi contacts amounts to 10A, being relatively large, so that it happens to cause a chopping surge in current interruption. Thus, a pair of the Cu-0.5 Bi contacts are low in interrupting capability of relatively small lagging current, which happens to lead to dielectric breakdown of electrical devices of load circuits.
To eliminate the drawbacks of the abovedescribed contacts, various contacts made of an alloy consisting of copper and material of high melting point and low vapor pressure, such as a contact of an alloy consisting of 20 weight % copper and 80 weight % tungsten (hereinafter, referred to as a 20Cu-80 W contact) that is disclosed by the U.S. Pat. No. 3,811,939, or a contact that is disclosed by U.K. Pat. No. 2,024,257A, are provided.
Such contacts made of an alloy consisting of copper and material of high melting point and low vapor pressure, for example, the 20Cu-80 W contact, are relatively high in dielectric strength; however, they are relatively low in large current interrupting capability.
Consequently, it is found that to increase current interrupting capability and high withstanding voltage for a vacuum interrupter will be difficult unless novel materials are provided.